OCR Text |
Show between layers decrease and the borders between layers become less clear. It is easy to differentiate snow layers in freezing weather because of the solid nature of the snow at low temperatures. With thawing, differences between layers become progressively less and less apparent, though important differences are still present, as can be observed by opening a cut in open snowcover to show where flowing melt water demarcating layers later freezes to form lines of icicles at different levels. When melt water freezes, the layers are clearly distinct once again. Differences in the amount of material composing snow layers and in their strength and condition may be clearly seen even at adjacent sites; in the early part of the winter, these differences are mostly due to wind action. On flat mountain tops open to winds from all directions, the layers are homogeneous in structure and easy to distinguish, even when the cover is thick. In deep gullies one can observe multiple layers of loose snow, not always well- differentiated. Some of such layers are measured in tens of centimeters. In unwooded valleys one observes multiple thin layers, often escalated. In thinly wooded areas the various layers are found to be more or less even in thickness and of homogeneous structure. Toward the end of winter, one can clearly distinguish the differences in snow condition in the large areas on slopes of differing exposure. The basic snowcover layers, laid down on a receptable plaque at a meteorological station during the winter of 1936- 37, are shown in Figure 1. Fresh snow f J Windblown snow Loose Fine granular Dense 7T7T- 3 ° Ql _ 3ooo Granular Loose Granu] Dense 5X1 16X11 25X11 16.1 2U. I1 UN ' 3IV Fiq. 1. Changes in Snowcover During Winter of 1936- 37. £_£) Coarse Granular V71 Moist | « # » I Wet Granular Ice Crust ( whole and disintegrating) Snow skin - 20- |